The present invention relates to a hitch control system for an agricultural vehicle.
Hitch control systems currently in use on agricultural tractors control the hitch in response to mechanically or hydraulically sensed draft force, mechanically sensed rockshaft position and operator-generated control signals. Typical of such systems are the mechanical draft control system shown in U.S. Pat. No. 3,455,397 and the hydraulic draft control system shown in U.S. Pat. No. 3,990,520. Such systems also can provide means for controlling the mixture ratio of signals representing draft force and hitch position so that the hitch is controlled as a function of a variable and selected mixture of both sensed draft force and sensed rockshaft position. For an example of such a selective system, see U.S. Pat. No. 2,921.638.
Also known in the prior art is a hitch control system (described in U.S. Pat. No. 3,374,842), which includes electrically sensed draft force (via a strain gauge), an electrical control circuit and a position-responsive valve control linkage. However, this system does not include conventional mechanical or hydraulic draft force sensing, nor does it disclose any means for combining electrically sensed wheel slip or engine speed with conventional non-electrical sensed draft force.
Other hitch control systems have been proposed to control a hitch or implement in response to sensed wheel slip and engine speed in addition to sensed draft force and rockshaft position. However, these systems have required electronic transducers to sense the draft force and the rockshaft position in place of the conventional hydraulic or mechanical position and draft sensing mechanisms currently in use, and therefore, cannot be retrofitted to conventional production hitch control systems. Accordingly, it would be desirable to provide a hybrid which control system wherein electrically sensed inputs, such as wheel slip and engine speed signals, are combined with the non-electrically sensed position and draft force inputs of current production hitch control systems.